Offer some examples of how human activities have affected bird populations.

Bird hunting caused huge problems for bird populations. Many species of birds were hunted to extinction, including the passenger pigeons. Lead bullets that littered the ground were mistaken for food by some birds and were eaten, causing lead poisoning.
Human agriculture is also causing a decline in song bird populations. Herbcides and pesticides used on fields make the field unusable to ground nesting birds. In addition, the deforestation for agriculture is leaving many birds open to attack from nest predators and parasites. Domesticated cats also present a large problem for many birds; they have been estimated to kill around 19 million song birds in a single year.
Deforestation of the rainforests is also depriving birds of their winter homes. Birds' migration patterns are being thrown off by lack of winter migratory destinations, causing a serious problem for many bird populations.
Not all human interactions were bad for birds; starlings and house sparrows have become the most abundant bird species on earth because they are spread by humans.